Unaudited Quarterly Consolidated Financial Information (Schedule Of Unaudited Quarterly Consolidated Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 187,417	$ 245,888	$ 323,828	$ 279,140	$ 208,678	$ 274,088	$ 345,671	$ 262,193	$ 1,036,273	$ 1,090,630	$ 1,198,223
Gross profit	78,724	122,434	169,640	129,366	72,744	120,821	189,870	127,370	500,164	510,805	590,345
Restructuring					1,274	981	2,810	3,663		8,728	24,517
Asset impairments	1,449	930	572	193	7,771	5,460	2,075	0	3,144	15,306	8,827
Income (loss) from operations	(39,787)	(1,215)	20,605	14,243	(65,581)	(20,730)	16,349	(2,362)	(6,154)	(72,324)	(4,726)
Net loss	(40,644)	(1,533)	15,537	10,146	(70,173)	(24,024)	13,426	(2,425)	(16,494)	(83,196)	(4,926)
Net loss attributable to common stockholders—basic and diluted	$ (44,482)	$ (5,352)	$ 11,735	$ 6,361	$ (73,942)	$ (27,776)	$ 9,690	$ (5,979)	$ (31,738)	$ (98,007)	$ (18,962)
Basic income (loss) per common share (in dollars per share)	$ (0.60)	$ (0.07)	$ 0.13	$ 0.07	$ (1.01)	$ (0.37)	$ 0.11	$ (0.08)	$ (0.43)	$ (1.30)	$ (0.22)
Diluted income (loss) per common share (in dollars per share)	$ (0.60)	$ (0.07)	$ 0.13	$ 0.07	$ (1.01)	$ (0.37)	$ 0.11	$ (0.08)	$ (0.43)	$ (1.30)	$ (0.22)